Related Person Transactions (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended		1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended					3 Months Ended		9 Months Ended		1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended			1 Months Ended		5 Months Ended	9 Months Ended	1 Months Ended					3 Months Ended	9 Months Ended
	Sep. 30, 2011 property segment Y count state	Sep. 30, 2010	Sep. 30, 2011 property segment Y count state	Sep. 30, 2010	Jul. 31, 2011 Acquisition Five Star Senior living communities Six States property	Sep. 30, 2011 Five Star officer person	Sep. 30, 2010 Five Star	Sep. 30, 2011 Five Star officer person	Sep. 30, 2010 Five Star	Dec. 31, 2010 Five Star	Oct. 28, 2011 Five Star	May 31, 2011 Five Star	Sep. 30, 2011 Five Star Senior living communities property	Sep. 30, 2011 Five Star Rehabilitation hospitals property	Sep. 30, 2011 RMR	Sep. 30, 2010 RMR	Sep. 30, 2011 RMR	Sep. 30, 2010 RMR	Jun. 30, 2011 AIC Y	Sep. 30, 2011 AIC company	Sep. 30, 2010 AIC	Sep. 30, 2011 AIC company	Sep. 30, 2010 AIC	May 31, 2012 AIC	May 31, 2011 AIC	Dec. 31, 2010 AIC	Sep. 30, 2011 Acquisition CommonWealth REIT (CWH) Medical Office Building property sqft state	Sep. 30, 2011 CommonWealth REIT (CWH)	Sep. 30, 2011 Acquisition sqft agreement	Sep. 30, 2011 Acquisition	Aug. 31, 2011 Acquisition Senior living communities Five States in the southeastern United States property	Jul. 31, 2011 Acquisition Senior living communities Five States in the southeastern United States property	Jun. 30, 2011 Acquisition Senior living communities Five States in the southeastern United States property	May 31, 2011 Acquisition Senior living communities Five States in the southeastern United States property	Mar. 31, 2011 Acquisition Senior living communities Five States in the southeastern United States property state	Sep. 30, 2011 Acquisition Senior living communities Five States in the southeastern United States	Sep. 30, 2011 Acquisition Senior living communities Five States in the southeastern United States property	Sep. 30, 2011 Acquisition Senior living communities Six States state
Related person transactions
Investment in common shares (in shares)						4,235,000		4,235,000																				250,000
Percentage of total shares outstanding (as a percent)						8.90%		8.90%
Earnings and losses recognized related to equity investments	$ 28	$ 35	$ 111	$ (17)																$ 28	$ 35	$ 111	$ (17)
Number of Managing Trustees also serving as managing directors						1		1
Number of real estate properties leased													188	2
Minimum annual rent payable to entity								194,598																													6,984
Total rent recognized						48,392	46,388	141,875	138,698
Rents receivable						17,434		17,434		16,762
Number of properties agreed to be acquired					9																						13								20		2
Amount agreed to be lent under Bridge Loan Agreement												80,000
Aggregate principal amount outstanding under Bridge Loan						48,000		48,000			48,000
Number of states in which properties are located	37		37																								8								5			6
Aggregate purchase price of properties acquired, excluding closing costs					478,000																						167,000		43,725	569,893	17,158	44,671	196,594		304,000
Number of properties acquired																															1	3	14
Area of real estate properties acquired (in square feet)																											1,300,000		138,606
Interest and other income	462	203	971	703		187		245
Mortgage loans expected to be assumed in real estate acquisition																													9,700	9,700
Number of properties agreed to be acquired, referred as managed properties					9																													15
Number of properties agreed to be acquired, referred as leased properties					8																																5
Number of properties acquired, referred as managed properties																															1	2	10
Number of executive officers also serving as officers of RMR						3		3
Real estate improvements purchased						10,554		25,877		31,894
Increase or decrease in annual lease rent payable						845		2,073
Business management agreement expense															4,865	4,317	15,241	12,715																		326	351
Property management agreement expense															1,111	561	3,193	1,665
Beneficial ownership of common shares (as a percent)																												100.00%
Equity method investments, ownership percentage (as a percent)																				14.29%		14.29%
Number of other companies which are shareholders of related party																				5		5
The entity owns less than this percentage of an equity method investment (as a percent)																				20.00%		20.00%
Amount invested in equity investee																				5,209		5,209
Equity method investments, carrying value																				5,245		5,245				5,076
Period for which property insurance program was extended (in years)																			1
Total premiums																								$ 1,170	$ 275